Thank you Gaetan, This was very helpful. I saw that the primary/secondaryjoin arguments could be callable, but I didn't connect that with the approach that you used in the example. Also thank you for clarifying the remote and local_side arguments.
Best, Stephen. On Wed, Oct 29, 2008 at 12:23 PM, Gaetan de Menten <[EMAIL PROTECTED]>wrote: > On Wed, Oct 29, 2008 at 3:23 PM, Gaetan de Menten <[EMAIL PROTECTED]> > wrote: > > On Wed, Oct 29, 2008 at 1:22 AM, Stephen Soltesz > > <[EMAIL PROTECTED]> wrote: > >> Hello, I'm experiencing an issue nearly identical in structure as that > in a > >> recent post: > >> > >> > http://groups.google.com/group/sqlelixir/browse_thread/thread/ed8d0650b79ce942 > >> > >> The raw sqlalchemy version works without exception. But, my preference > is > >> to simply use Elixir to do this, yet I find that I'm pulling my hair out > >> trying to figure it out. > >> I am using Elixir - 0.6.1 and SA 0.5.0rc1. > >> > >> I've attached a simple test case that creates the tables in a postgres > db. > >> > >> Can anyone provide a hint for what the correct translation is into > Elixir > >> from the code in the attached example? > >> > >> For the Elixir version, is there a way to reference the ClauseElements > in > >> the primaryjoin= & secondaryjoin= values in the same way as I do in the > SA > >> version? > >> > >> As is, the Elixir version raises: > >> sqlalchemy.exc.ArgumentError: Could not determine join condition > between > >> parent/child tables on relation UsrGrp.users. Specify a 'primaryjoin' > >> expression. If this is a many-to-many relation, 'secondaryjoin' is > needed > >> as well. > >> > >> Thank you very much for any hints you can provide. > >> Stephen. > > > > Well, the short answer is: this is not currently possible, due to > > several reasons. A longer answer will follow after I have researched > > if I can fix this easily or not. > > Strike that. There is an undocumented feature of SA 0.5 (not sure > exactly when it was introduced since it's not documented) which makes > it work/possible even with Elixir 0.6.1... See below for details... > > First, the problem: > - SA usually computes the primaryjoin and secondaryjoin clauses > automatically in most cases, and Elixir does it in addition for > self-referencial relationships which SA doesn't handle automatically. > This is done by introspecting the ForeignKey constraint defined on the > tables. Since your tables don't have any, you have to define all this > stuff manually. It seems like you figured that much. > - Those conditions need to be expressed as > column_object==another_column_obect, which means you need access to > the columns of your tables. The problem is that when using Elixir and > not explicit tables, those column object do not exist at the time of > class definition. The solution I choose to use for Elixir, is to allow > those arguments to be passed as callables which are then evaluated > when the table has been loaded or created. There is one more problem: > how do you access the columns of your intermediary table since you > have neither an explicit table object, nor an Entity for it. There are > two solutions here: either, you use an ugly Elixir-only hack > (commented in the attached code), or you use an "hybrid" approach, > that is you autoload the ManyToMany intermediary table explicitly, and > use that table object in the ManyToMany relationship (instead of the > name of that table). The later approach is much cleaner IMO. > - I thought your precise use case was impossible, because in 0.6.1, > Elixir didn't translate/call the foreign_keys argument if it is a > callable and you need to specify it (because you don't have any in > your table). But the good surprise of the day is that SA0.5 also > accepts a callable for that argument, even if it is not documented. > > See attached script for a working example. > > PS: > - even in your SA-only example, the foreign_keys argument you pass is > wrong: it should only contain 2 columns... > - you don't need to specify local_side and remote_side. This was only > needed for self-referencial relationships (even if the doc doesn't > mention it). And it should only be needed if you don't specify manual > primary_join or secondary_join. I've just fixed these two issues (the > doc issue and this one) in trunk. > > Hope it helps, > -- > Gaëtan de Menten > http://openhex.org > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "SQLElixir" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlelixir?hl=en -~----------~----~----~----~------~----~------~--~---
